From Wiki -
"The file is an optional file used to and handle application and session-level events and objects for an ASP.NET web site running on an IIS Web Server. The file contains ASP.NET program code, and is the .NET counterpart of the Global.asa file used for ASP. The Global.asax file resides in the IIS virtual root of an ASP.NET application."
Effectively, global.asax allows you to write code that runs in response to "system level" events, such as the application starting, a session ending, an application error occurring, without having to try and shoe-horn that code into each and every page of your site.
You can use it by by choosing Add > New Item > Global Application Class in Visual Studio. Once you've added the file, you can add code under any of the events that are listed (and created by default, at least in Visual Studio 2008):
- Application_Start
- Application_End
- Session_Start
- Session_End
- Application_BeginRequest
- Application_AuthenticateRequest
- Application_Error
There are other events that you can also hook into, such as "LogRequest".
